Sensor and guide wire assemblies in which a sensor, adapted for measurements of physiological variables in a living body, such as blood pressure and temperature, is mounted at a distal portion of a guide wire are known.
For example, the U.S. Pat. No. Re. 35,648, which is assigned to the present assignee, discloses a sensor and guide wire assembly comprising a sensor element, an electronic unit, signal transmitting cables connecting the sensor element to the electronic unit, a flexible tube having the signal cables and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements electrically connected in a Wheatstone bridge-type of circuit arrangement mounted thereon. The entire contents of the '648 patent are incorporated herein by reference for additional details of equipment, methods, and techniques for such measurements.
The sensor element is usually provided in the form of a silicon chip, which besides the pressure sensitive device also comprises integrated electronic circuits. For various reasons it is desired to include ever more functionality in the electronic circuits. This need has so far been met by the general miniaturization trend that exists in the chip technology, which allows more functionality and more complex circuits to be integrated in a comparatively smaller area, or, in the three-dimensional case, in a smaller volume. Such miniaturization is extremely important within the field of guide wire mounted sensors, because the outer diameter of the sensor guide wire is in practice limited by the inner diameter of a catheter which in a so-called PCI (Percutan Coronar Intervention) is used for the treatment of a stenosis present in a blood vessel and which is threaded over the sensor guide wire and advanced to the site of interest. The standard inner diameter of such catheters is 0.35 mm (0.014 inches); and consequently the standard outer diameter of most guide wires, and in particular of sensor guide wires, is therefore 0.35 mm (0.014 inches).
However, the miniaturization of electronic circuits and chips is a difficult task, and it is far from certain that the chips industry can provide sensor chips which fulfil the future requirements for mounting in a guide wire adapted for intravascular measurements.
Consequently, there is a need for a guide wire design that provides more space for a sensor element, while at the same time allows use together with a standard catheter.